The present invention relates generally to prostheses for implantation with body lumens, and more particularly to a stent-graft having a flexible exo-skeleton slidably attached to a tubular graft.
Graft prostheses are often implanted within blood vessels, particularly the aorta or other arteries, which may be subject to aneurysm formation and/or severe atherosclerotic disease which may involve multiple stenoses. For example, an aortic aneurysm may develop in a patient, for example, within the abdominal aorta at the aorto-iliac bifurcation, requiring treatment before the vessel wall ruptures. To repair a blood vessel damaged by such an affliction, a procedure involving use of a graft prosthesis is generally performed.
A number of graft prostheses have been suggested that include a tubular graft attached to a stent. The tubular graft may be a biocompatible porous or nonporous tubular structure to which a stent structure, such as a wire mesh, may be attached. The stent structure may be biased to assume an enlarged configuration corresponding to a target treatment site, but may be constrained in a contracted condition to facilitate introduction into a patient""s vasculature. The graft prosthesis may be percutaneously introduced in the contracted condition, advanced to a treatment site within a blood vessel, and released to assume the enlarged condition and repair and/or bypass the treatment site.
One problem often associated with such prostheses is effectively securing the tubular graft at the treatment site. The released graft prosthesis may not sufficiently engage the vessel wall adjacent the treatment site, possibly resulting in the graft prosthesis moving after implantation, which may expose the damaged vessel wall. Plastically deformable expandable stent structures may be provided to attempt to more directly control the engagement between the graft prosthesis and the vessel wall. Such plastically deformable structures, however, may not provide desired flexibility transverse to the longitudinal axis of the stent, making direction through and/or implantation within tortuous body passages difficult. Further, they also generally require the use of a balloon or other expandable member to expand the stent structure to the enlarged condition, which may introduce risks of uneven stent structure expansion and/or balloon rupture.
In addition to plastically deformable stents, coiled-sheet stent structures have been suggested. Coiled-sheet stents may provide enhanced anchoring within the blood vessel because the size of the fully expanded stent may be more precisely controlled. Coiled sheet stents may be substantially evenly expanded and generally do not involve plastic deformation of the stent material. A coiled-sheet stent, however, may be substantially rigid transverse to its longitudinal axis, potentially resulting in a less flexible graft prosthesis, which may not be implanted effectively in tortuous anatomical conditions.
Graft prostheses may also be vulnerable when subjected to longitudinal compression, which is often encountered after implantation. The vessel wall may at least partially recover after a graft has been implanted and the underlying vessel wall no longer experiences substantial blood pressure. If the vessel wall shortens longitudinally during recovery, it may cause the graft material to buckle and kink, thereby potentially constricting flow through the graft prosthesis.
Therefore, there is a need for an-improved stent-graft that may provide improved flexibility and/or graft support, while still providing substantial anchoring within a blood vessel.
The present invention is directed to a stent-graft having an exo-skeleton attached to a tubular graft. In accordance with one aspect of the present invention, a stent-graft is provided that includes a tubular graft having a peripheral wall defining a periphery and a lumen therein, the lumen extending axially between first and second ends of the tubular graft. An exo-skeleton is attached to the peripheral wall, the exo-skeleton including one or more serpentine elements, each serpentine element extending both peripherally, i.e., in a manner which generally surrounds the wall which may be circular, elliptical or other suitable configuration, and axially along at least a portion of the peripheral wall. A stent is provided on the first and/or second ends for substantially anchoring the ends within a body passage.
In a preferred form, each serpentine element is a zigzag structure extending peripherally about the peripheral wall of the tubular graft. More preferably, a plurality of serpentine elements are distributed axially along the peripheral wall for providing articulation of the tubular graft between adjacent serpentine elements. The serpentine elements may be individually attached to the peripheral wall and/or the serpentine elements may be connected to one another by one or more connector elements extending between adjacent serpentine elements.
In another preferred form, each serpentine element defines a generally sinusoidal shape extending axially along the peripheral wall. Preferably, a plurality of serpentine elements may distributed substantially evenly about the periphery of the peripheral wall. Each of these serpentine elements preferably includes substantially transverse peripheral elements, adjacent transverse peripheral elements being connected by alternating curved elements, thereby defining the generally sinusoidal shape.
The exo-skeleton of the stent-graft is preferably directable between a contracted condition for facilitating introduction within a body passage and an enlarged condition for deployment within the body passage. The exo-skeleton may substantially support the tubular graft to hold the lumen of the tubular graft substantially open in the enlarged condition. In a preferred form, the exo-skeleton is radially compressible to the contracted condition and biased to assume the enlarged condition. Alternatively, the contracted condition of the exo-skeleton may be achieved by flattening and circumferentially rolling the exo-skeleton.
The tubular graft may be provided from a polymeric material, such as polyester, polytetrafluorethaline, dacron, teflon, and polyurethane. The exo-skeleton may be attached to the tubular graft by sutures, staples, wires, or an adhesive, or alternatively by thermal bonding, chemical bonding, and ultrasonic bonding. The exo-skeleton may be formed from a metallic material, such as stainless steel or Nitinol, and may be a flat-coiled sheet with the one or more serpentine elements formed therein, or a wire formed into a serpentine shape.
In alternative forms, the first and second ends of the tubular graft may have similar cross-sections, or the first end of the tubular graft may have a cross-section that is substantially smaller than a cross-section of the second end of the tubular graft. In addition, the exo-skeleton may be attached to an exterior surface of the tubular graft, to an interior surface of the tubular graft, or embedded in the wall of the tubular graft.
In accordance with another aspect of the present invention, a stent-graft is provided for placement within a bifurcation that includes a first tubular graft segment having a first end and a second bifurcated end, the first tubular graft segment having a first peripheral wall. A second tubular graft segment extends from the second bifurcated end, the second tubular graft segment having a second peripheral wall. An exo-skeleton is attached to at least one of the first and second peripheral walls, the exo-skeleton including one or more serpentine elements, each serpentine element extending both peripherally and axially along at least a portion of the respective peripheral wall to which it is attached.
A coiled-sheet stent may be provided on the first end for substantially anchoring the first end within a body passage. Similarly, a coiled-sheet stent may be provided on the second tubular graft segment opposite the second end of the first tubular graft segment.
Preferably, the stent-graft also includes a third tubular graft segment attachable to the second bifurcated end, the third tubular graft segment having a third peripheral wall. The exo-skeleton also may include one or more serpentine elements attached to the third peripheral wall.
In accordance with still another aspect of the present invention, a stent-graft having a slidable exo-skeleton is provided. The stent graft includes a tubular graft having a wall defining a circumference or other periphery and a lumen therein, the lumen extending axially between first and second open ends of the tubular graft. One or more support elements are attached to the tubular graft, each support element extending generally peripherally around the tubular graft, each support element including generally axial segments and generally circumferential or peripheral segments. A plurality of first fasteners are provided for attaching the plurality of support elements to the wall of the tubular graft, at least one generally axial segment being slidably engaged by each first fastener. In addition, a plurality of second fasteners may also be provided for attaching the plurality of support elements to the wall of the tubular graft, each second fastener substantially anchoring a segment of the respective support element to the wall of the tubular graft. In a preferred form, the stent-graft also includes a first stent on the first end and/or a second stent on the second end for substantially anchoring the respective first and/or second ends within a body passage.
In one form, a set of first fasteners, such as sutures, staples or wires, is attached to respective first wall regions of the tubular graft, each first fastener slidably securing one or more axial segments therein, whereby the axial segments slidably secured by each first fastener may slide axially with respect to the respective first wall region. More preferably, each first fastener may slidably secure at least two axial segments of adjacent support elements to a respective wall region, whereby the two axial segments may independently slide axially with respect to the respective first wall region and/or with respect to each other. Preferably, a set of second fasteners is attached to respective second wall regions of the tubular graft, each second fastener substantially anchoring a peripheral segment to the respective second wall region.
Thus, a stent-graft in accordance with the present invention may have a substantially flexible region that may conform substantially to the anatomy of a treatment site. Preferably, the flexible region is defined by an exo-skeleton attached to a tubular graft that includes one or more serpentine elements. The serpentine elements may facilitate articulation between adjacent serpentine elements, and/or may be sufficiently resilient and flexible to allow articulation, compression and/or expansion of the serpentine elements themselves.
Preferably, the stent-graft also includes sealing members, preferably coiled-sheet stents, attached to the ends of the tubular graft for substantially sealing and/or anchoring the ends of the tubular graft proximate the treatment site. Thus, the stent-graft may accommodate tortuous anatomy while still providing effective sealing and anchoring within a body passage.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.